Trazodone and trazodone hydrochloride in purified form

ABSTRACT

A process of production of trazodone or trazodone hydrochloride that comprises: (a) preparing an organic phase comprising trazodone in at least one organic solvent; (b) preparing an aqueous phase comprising at least one basic compound; (c) mixing said aqueous phase with said organic phase; (d) heating at a temperature of at least 40° C. for at least 30 minutes; (e) recovering said trazodone; and, optionally, (f) treating said trazodone with hydrochloric acid to obtain trazodone hydrochloride. Trazodone or trazodone hydrochloride comprising less than 15 ppm of alkylating substances, and a pharmaceutical composition comprising said trazodone hydrochloride.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.12/513,048, filed on Sep. 21, 2009, which was a 371 of InternationalPatent Application No. PCT/EP08/59640, filed on Jul. 23, 2008, andclaims priority to U.S. Provisional Patent Application No. 60/976,535,filed on Oct. 1, 2007, and Italian Patent Application No. MI2007A001603, filed on Aug. 3, 2007.

FIELD OF THE INVENTION

The present invention relates to a purified form of trazodone andtrazodone hydrochloride, and the process for preparation thereof.

In particular the invention relates to a purified form of trazodone andtrazodone hydrochloride comprising less than 15 ppm of alkylatingsubstances of proven or suspected genotoxicity.

PRIOR ART

Trazodone, or2-[3-[4-(3-chlorophenyl)-1-piperazinylpropyl]-1,2,4-triazolo[4,3-a]pyridin-3(2H)-one,is an antidepressant which, though having a significant effect on theserotonin receptors, is neither a psychostimulant, nor a MAO inhibitor,nor a tricyclic antidepressant. Furthermore, trazodone possessesanalgesic properties.

Trazodone alleviates the characteristic symptoms of depression, inparticular anxiety, somatization, psychomotor retardation, hypochondria,mood swings, irritability, insomnia, apathy, feeling of fatigue and lackof energy, depressed mood.

Trazodone has also proved effective in controlling pronounced essentialtremor, probably on account of its serotoninergic activity.

Moreover, the antidepressant and anxiolytic properties of trazodone haveproved useful in the treatment of symptoms of withdrawal from cocaine,benzodiazepines and alcohol. Besides the above-mentioned activities, itssleep-inducing activity is also very interesting.

Trazodone is preferably used medically in the form of a pharmaceuticallyacceptable salt of acid addition. The preferred form is thehydrochloride form obtained by treatment of the free base withhydrochloric acid.

Trazodone hydrochloride is represented by the following structuralformula:

Some economically advantageous methods of preparation of trazodonehydrochloride are described in U.S. Pat. No. 3,381,009 and EP 1,108,722.

A first method comprises reacting s-triazolo-[4,3-a]-pyridin-3-one offormula I with N-(3-chlorophenyl)-N′-(3-chloropropyl)-piperazine offormula II:

A second method comprises reacting2-(3-chloropropyl)-s-triazolo-[4,3-a]-pyridin-3-one of formula III withN-(3-chlorophenyl)-piperazine of formula IV:

A third method comprises reacting2-(γ-morpholino-propyl)-s-triazolo-[4,3-a]-pyridin-3-one of formula Vwith 3-chloroaniline of formula VI

A fourth method comprises reacting2-(3-aminopropyl)-s-triazolo[4,3-a]-pyridin-3-one of formula VII with3-chloro-N,N′-dichloroethylaniline of formula VIII:

A fifth method comprises reacting2-{3-[bis-(2-chloroethyl)-amino]-propyl}2H-[1,2,4]triazolo[4,3-a]pyridin-3-oneof formula IX with 3-chloroaniline of formula VI.

Once trazodone has been obtained, trazodone hydrochloride is easilyobtained by reaction with hydrochloric acid, for example by treating anorganic solution of trazodone with an aqueous solution of hydrochloricacid, as described for example in patent EP 1,108,722.

Preparation of the aforementioned intermediates from I to IX requiresthe use of alkylating substances of proven genotoxicity, such as2,2-dichloroethylamine, used for obtaining compound IV by reaction withcompound VI; 1-bromo-3-chloropropane, used for obtaining compound II byreaction with compound IV.

Compounds II, III, VIII and IX are also alkylating substances andtherefore potentially genotoxic. Apart from the aforementionedalkylating substances, in alternative processes for production oftrazodone it may be possible to use similar alkylating substances, forexample 2,2-dibromoethylamine or 1,3-dichloropropane.

The content of said alkylating substances in the final product,represented by trazodone and trazodone hydrochloride, should be reducedto the least possible amount. In particular, the toxicological thresholdfor ingestion of these alkylating substances has been determined as 1.5μg per day.

Therefore, assuming a daily dose of 100 mg of trazodone hydrochloride,the quantity of alkylating substances present as impurities in theproduct should be less than 15 ppm. If, however, we consider the maximumdaily dose of 600 mg of trazodone hydrochloride, the quantity ofalkylating substances present as impurities in the product should evenbe less than 2.5 ppm.

Unfortunately, the processes of preparation described in theaforementioned patents U.S. Pat. No. 3,381,009 and EP 1,108,722 do notallow the content of these alkylating substances to be reduced to below15 ppm, let alone below 2.5 ppm.

Therefore, the applicant tackled the problem of devising a process forproduction of trazodone and trazodone hydrochloride that makes itpossible to lower the content of these alkylating substances in thefinal product to below 15 ppm. Moreover, said production process must beeconomically advantageous and must give high yields of final product.

DEFINITIONS

In the present description and in the claims given later, the expression“trazodone” means trazodone in the form of free base, whereas theexpression “trazodone hydrochloride” means the salt formed by theaddition of hydrochloric acid to trazodone.

Moreover, in the present description and in the claims given later, theexpression “alkylating substances” is used to indicate substances thatare capable of introducing an alkyl group in a compound used in thesynthesis of trazodone or of an intermediate thereof.

DESCRIPTION OF THE INVENTION

Surprisingly, the applicant found that addition of an aqueous solutioncomprising a basic compound to a solution of trazodone in an organicsolvent reduces the amount of alkylating substances in the final productto below 15 ppm.

Therefore, the present invention relates to a production process oftrazodone or of trazodone hydrochloride that comprises the steps of:

(a) preparing an organic phase comprising trazodone in at least oneorganic solvent;

(b) preparing an aqueous phase comprising at least one basic compound;

(c) mixing said aqueous phase with said organic phase;

(d) heating at a temperature of at least 40° C. for at least 30 minutes;

(e) recovering said trazodone; and, optionally

(f) treating said trazodone with hydrochloric acid to obtain trazodonehydrochloride.

The production process of the present invention makes it possible toreduce the amount of alkylating substances in the final product,represented by trazodone or by trazodone hydrochloride, to below 15 ppm,preferably below 10 ppm, and more preferably below 2.5 ppm.

Advantageously, according to a preferred aspect of the presentinvention, the production process of the present invention makes itpossible to reduce the amount of alkylating substances in the finalproduct to below 1 ppm.

The process of the present invention has been shown to be economicallyadvantageous, keeping the yield of the final product above 85%, andpreferably above 90%.

Preferably said organic phase is represented by a solution of trazodonein said organic solvent.

Advantageously, said organic solvent can be selected from any organicsolvents that are inert with respect to trazodone and that are able todissolve trazodone.

Preferably, said organic solvent is selected from the group comprisingalcohols, for example, ethyl alcohol, propyl alcohol, isobutyl alcohol,hexyl alcohol, and benzyl alcohol; ethers, for example ethyl ether,propyl ether; hydrocarbons, for example toluene, benzene, xylene;ketones, for example acetone, methyl ethyl ketone, methyl isobutylketone; esters, for example ethyl acetate. The preferred organic solventfor preparation of the organic phase is isobutyl alcohol.

Preferably, said organic phase comprises an amount of trazodone in therange from 10 g to 50 g per 100 grams of organic phase, more preferablyfrom 20 g to 35 g per 100 grams of organic phase, and even morepreferably from 25 g to 30 g per 100 grams of organic phase.

Preferably said aqueous phase is represented by a solution of a basiccompound in water.

Advantageously, said aqueous phase comprises at least one basic compoundselected from the group comprising at least one inorganic base, at leastone organic base, or mixtures thereof.

Useful examples of inorganic bases are sodium hydroxide, potassiumhydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate,potassium bicarbonate, sodium phosphate, potassium phosphate, ammoniumhydroxide, magnesium oxide, hydrazine, and hydroxylamine.

Useful examples of organic bases are aliphatic or aromatic amines, forexample methylamine, ethylamine, propylamine, butylamine, diethylamine,trimethylamine, triethylamine, ethanolamine, diethanolamine,triethanolamine, N,N-dimethylethanolamine, N-methylethanolamine,ethylenediamine, piperidine, quinoline, imidazole, benzimidazole,histidine, pyridine, picoline, lutidine, collidine, morpholine,N-methylmorpholine, benzylamine, and cyclohexylamine.

Preferably, said basic compound is added in an amount in the range from0.05 to 1 mol per mol of trazodone, more preferably from 0.2 to 0.8 molper mol of trazodone, and even more preferably from 0.4 to 0.6 mol permol of trazodone.

Advantageously, said aqueous phase is added in an amount in the rangefrom 30 g to 100 g per 100 grams of organic phase, more preferably from40 g to 90 g per 100 grams of organic phase, and even more preferablyfrom 50 g to 80 g per 100 grams of organic phase.

Preferably, said aqueous phase comprises a phase transfer catalyst.

Advantageously, said phase transfer catalyst is selected from the groupcomprising quaternary ammonium salts and quaternary phosphonium salts.

Preferably, said quaternary ammonium salts are selected from the groupcomprising benzyl tributyl ammonium bromide, benzyl tributyl ammoniumchloride, benzyl triethyl ammonium bromide, benzyl triethyl ammoniumchloride, benzyl trimethyl ammonium chloride, cetyl pyridinium bromide,cetyl pyridinium chloride, cetyl trimethyl ammonium bromide, didecyldimethyl ammonium chloride, dodecyl trimethyl ammonium bromide, dodecyltrimethyl ammonium chloride, methyl tributyl ammonium chloride, methyltributyl ammonium hydrogen sulphate, methyl tricaprilyl ammoniumchloride, methyl trioctyl ammonium chloride, phenyl trimethyl ammoniumchloride, tetrabutyl ammonium borohydride, tetrabutyl ammonium bromide,tetrabutyl ammonium chloride, tetrabutyl ammonium fluoride, tetra butylammonium hydrogen sulphate, tetrabutyl ammonium hydroxide, tetrabutylammonium iodide, tetrabutyl ammonium perchlorate, tetraethyl ammoniumbromide, tetraethyl ammonium chloride, tetraethyl ammonium hydroxide,tetrahexyl ammonium bromide, tetrahexyl ammonium iodide, tetramethylammonium bromide, tetramethyl ammonium chloride, tetramethyl ammoniumfluoride, tetramethyl ammonium hydroxide, tetramethyl ammonium iodide,tetraoctyl ammonium bromide, tetrapropyl ammonium bromide, tetrapropylammonium chloride, tetrapropyl ammonium hydroxide, tributyl methylammonium chloride, triethyl benzyl ammonium chloride.

Advantageously, said quaternary ammonium salts are selected from thegroup comprising tetrabutyl ammonium bromide, tetrabutyl ammoniumchloride, benzyl triethyl ammonium bromide, benzyl triethyl ammoniumchloride, benzyl trimethyl ammonium chloride, benzyl trimethyl ammoniumbromide, benzyl tributyl ammonium bromide, and benzyl tributyl ammoniumchloride.

The series of phase transfer catalysts Aliquat® produced and marketed bythe company Cognis Corp., Tucson, Ariz. can be used advantageously inthe production process of the present invention. Preferred examples areAliquat® 100, Aliquat® 134, Aliquat® 175, and Aliquat® 336.

Preferably, said quaternary phosphonium salts are selected from thegroup comprising benzyl triphenyl phosphonium bromide, benzyl triphenylphosphonium chloride, butyl triphenyl phosphonium bromide, butyltriphenyl phosphonium chloride, ethyl triphenyl phosphonium acetate,ethyl triphenyl phosphonium bromide, ethyl triphenyl phosphonium iodide,hexadecyl tributyl phosphonium bromide, methyl triphenyl phosphoniumbromide, tetrabutyl phosphonium bromide, and tetraphenyl phosphoniumbromide.

Preferably, said aqueous phase comprises an amount of phase transfercatalyst in the range from 0.05 g to 0.5 g per 100 grams of aqueousphase, more preferably from 0.1 g to 0.3 g per 100 grams of aqueousphase, and even more preferably from 0.15 g to 0.2 g per 100 grams ofaqueous phase.

Preferably, said heating step (d) is carried out at a temperaturebetween 40° and the boiling point of the mixture of organic phase andaqueous phase, for a period of time between 30 minutes and 300 minutes,preferably between 60 and 240 minutes, more preferably between 90 and180 minutes.

Preferably, the recovery step (e) is carried out by separating theaqueous phase from the organic phase comprising the trazodone, andcooling the latter to a temperature below 30° C., preferably below 20°C., and even more preferably below 10° C., to promote thecrystallization and precipitation of trazodone, which is finallyseparated, for example by filtration.

Advantageously, in the final treatment step (f), the trazodone ispreferably dissolved in a suitable organic solvent, selected, forexample, from those stated previously for the preparation of the organicphase. The solvent preferred in this step is acetone. The solution thusobtained is treated with an aqueous solution of hydrochloric acid asdescribed in patent EP 1,108,722. The precipitate of trazodonehydrochloride is then filtered, washed, and dried according to theconventional techniques known by a person skilled in the art.

The trazodone and the trazodone hydrochloride obtained by the process ofthe present invention are characterized by a content of alkylatingsubstances, of proven or suspected genotoxicity, below 15 ppm.

Depending on the production process selected for the production oftrazodone and of trazodone hydrochloride, the alkylating substancespresent as impurities are, for example, 2,2-dichloromethylamine,1-bromo-3-chloro-propane,N-(3-chlorophenyl)-N′-(3-chloropropyl)-piperazine (formula II),2-(3-chloropropyl)-s-triazolo-[4,3-a]-pyridin-3-one (formula III),3-chloro-N,N′-dichloroethyl-aniline (formula VIII),2-{3-[bis-(2-chloroethyl)-amino]-propyl}-2H-[1,2,4]triazolo[4,3-a]pyridin-3-one(formula IX), 2,2-dibromoethylamine, and 1,3-dichloropropane.

In particular, the alkylating substances encountered most frequently arerepresented by 2,2-dichloroethylamine, 1-bromo-3-chloro-propane, andN-(3-chlorophenyl)-N′-(3-chloropropyl)-piperazine.

2,2-Dichloroethylamine (CAS No. 334-22-5) and 1-bromo-3-chloro-propane(CAS No. 109-70-6) are known genotoxic substances as reported in TOXNET,a database published by the National Library of Medicine, US on thewebsite http://toxnet.nlm.nih.gov/.

The genotoxic activity ofN-(3-chlorophenyl)-N′-(3-chloropropyl)-piperazine has been assessed onhistidine-dependent auxotrophic mutants of Salmonella typhimuriumstrains TA1535, TA1537, TA 98 and TA100, and on tryptophan-dependentmutants of Escherichia coli strain WP2 uvrA (pKM101), exposed to asolution of N-(3-chlorophenyl)-N′-(3-chloropropyl)-piperazine indimethylsulphoxide (DMSO) and using DMSO as negative control. Twoindependent mutation tests were performed, both in the presence andabsence of a liver microsomal fraction (S9 mix) of rat treated withphenobarbital and 5,6-benzoflavone. Tests were standard plateincorporation assays and performed according to the current regulatoryguidelines. A substantial increase in reversion to prototrophy wasobtained on strain TA1535 in the presence of S9 mix. In the two assaysthe increase was concentration related and reached, following exposureto 1500 μg per plate ofN-(3-chlorophenyl)-N′-(3-chloropropyl)-piperazine, 6.4 and 5.1 times thecontrol value. It was therefore concluded thatN-(3-chlorophenyl)-N′-(3-chloropropyl)-piperazine exhibited genotoxicactivity in said bacterial system following metabolic activation.

Surprisingly, the total content of said alkylating substances in thetrazodone or in the trazodone hydrochloride obtained using the processof the present invention was below 15 ppm, preferably less than 10 ppm,and even more preferably less than 2.5 ppm. In the preferred embodiment,the content of each of said alkylating substances in the trazodone or inthe trazodone hydrochloride obtained using the process of the presentinvention was below 1 ppm.

Therefore, the present invention also relates to trazodone or trazodonehydrochloride comprising less than 15 ppm of alkylating substances,preferably less than 10 ppm, and even more preferably less than 2.5 ppm.

In a preferred embodiment, the present invention also relates totrazodone or trazodone hydrochloride comprising less than 1 ppm, andpreferably less than 0.5 ppm, of each alkylating substance.

Preferably said alkylating substances are selected from the groupcomprising 2,2-dichloroethylamine, 1-bromo-3-chloro-propane; andN-(3-chloro-phenyl)-N′-(3-chloropropyl)-piperazine (formula II),2-(3-chloropropyl)-s-triazolo-[4,3-a]-pyridin-3-one (formula III),3-chloro-N,N′-dichloroethyl-aniline (formula VIII),2-{3-[bis-(2-chloroethyl)-amino]-propyl}-2H-[1,2,4]triazolo[4,3-a]pyridin-3-one(formula IX), 2,2-dibromoethylamine, and 1,3-dichloro-propane.

Even more preferably said alkylating substances are selected from thegroup comprising 2,2-dichloroethylamine, 1-bromo-3-chloropropane, andN-(3-chlorophenyl)-N′-(3-chloropropyl)-piperazine.

The trazodone hydrochloride of the present invention can be usedadvantageously in the preparation of pharmaceutical compositions mixedwith at least one pharmaceutically acceptable excipient.

Thus, the present invention also relates to a pharmaceutical compositioncomprising the trazodone hydrochloride of the present invention asdescribed previously together with at least one pharmaceuticallyacceptable excipient.

The term “pharmaceutically acceptable excipient” means, withoutparticular limitations, any material suitable for the preparation of apharmaceutical composition that is to be administered to a living being.

Such materials, known by a person skilled in the art, are for exampleantiadherents, binders, disintegrants, fillers, diluents, flavouringagents, colorants, fluidizers, lubricants, preservatives, moisteningagents, absorbents, and sweeteners.

Useful examples of pharmaceutically acceptable excipients are sugars,such as lactose, glucose or sucrose, starches, such as maize starch, andpotato starch, cellulose and derivatives thereof, such as sodiumcarboxymethylcellulose, ethylcellulose, and cellulose acetate, gumtragacanth, malt, gelatin, talc, cocoa butter, waxes, oils, such aspeanut oil, cottonseed oil, safflower oil, sesame oil, olive oil, maizeoil, and soya oil, glycols such as propylene glycols, polyols, such asglycerol, sorbitol, mannitol, and polyethylene glycol, esters, such asethyl oleate, and ethyl laurate, agar-agar, buffers, such as magnesiumhydroxide, and aluminium hydroxide, alginic acid, water, isotonicsolutions, ethanol, buffer solutions, polyesters, polycarbonates,polyanhydrides, and so on.

The pharmaceutical composition of the present invention can berepresented by any composition that can be used for administration ofthe trazodone hydrochloride of the present invention, preferablycompositions for oral or parenteral administration, for example tablets,lozenges, capsules, solutions, suspensions, dispersions, and syrups.

The invention is illustrated by the following examples, though withoutlimiting it.

EXAMPLE 1 Preparation in the Presence of a Strong Base (NaOH)

37.1 g of trazodone (equal to about 0.100 mol) obtained according toexample 1 of U.S. Pat. No. 3,381,009 was put in a 500-ml flask togetherwith 140 ml of isobutyl alcohol. Then 100 ml of an aqueous solution ofNaOH at 2% was added, and the resultant mixture was heated to about 80°C. and held at this temperature, with stirring, for about 3 hours.

Then the organic phase was separated from the aqueous phase and thenwashed with water. The residual water present in the organic phase wasremoved by azeotropic distillation. The resultant solution was cooled to5° C. to precipitate the crystals of trazodone base, which wereseparated by filtration.

The wet product (about 40 g) was dissolved in about 270 ml of acetone,heated until dissolution occurred, and then 12N HCl aqueous solution wasadded to the solution up to pH between 3 and 4 to salify the trazodonebase and obtain the corresponding hydrochloride.

The resultant solution was cooled to 5° C. to precipitate the crystalsof trazodone hydrochloride. The trazodone hydrochloride thus obtainedwas filtered, washed with acetone and dried at reduced pressure. At theend of drying, 35.5 g of trazodone hydrochloride was obtained (equal toabout 0.087 mol), at a product yield equal to about 87%.

TABLE 1 Alkylating substances N-(3- 1-bromo-3- chlorophenyl)-N′- 2,2-chloro- (3-chloropropyl)- dichloroethylamine propane piperazine Initialcontent 10 15 50 (ppm) Final content <0.46 <0.2 <0.04 (ppm)

EXAMPLE 2 Preparation in the Presence of Weak Base (Na₂CO₃)

37.1 g of trazodone (equal to about 0.100 mol) obtained according toexample 1 of U.S. Pat. No. 3,381,009 was put in a 500-ml flask togetherwith 140 ml of isobutyl alcohol. Then 100 ml of an aqueous solutioncontaining 5.3 g of Na₂CO₃ was added, and the resultant mixture washeated to about 80° C. and left at this temperature, with stirring, forabout 4 hours.

Then the organic phase was separated from the aqueous phase and thenwashed with water. The residual water present in the organic phase wasremoved by azeotropic distillation. The resultant solution was cooled to5° C. to precipitate the crystals of trazodone base, which wereseparated by filtration.

The wet product (about 42 g) was dissolved in about 270 ml of acetone,heated until dissolution occurred, and then a 12N HCl aqueous solutionwas added to the solution until the pH was between 3 and 4 to salify thetrazodone base and obtain the corresponding hydrochloride.

The resultant solution was cooled to 5° C. to precipitate the crystalsof trazodone hydrochloride. The trazodone hydrochloride thus obtainedwas filtered, washed with acetone and dried at reduced pressure. At theend of drying, 37.0 g of trazodone hydrochloride was obtained (equal toabout 0.091 mol), at a product yield equal to about 91%.

TABLE 2 Alkylating substances N-(3- 1-bromo-3- chlorophenyl)-N′- 2,2-chloro- (3-chloropropyl)- dichloroethylamine propane piperazine Initialcontent 5 20 35 (ppm) Final content <0.46 <0.2 <0.4 (ppm)

EXAMPLE 3 Preparation in the Presence of Weak Base (Na₂CO₃) and PhaseTransfer Catalyst (Benzyltriethylammonium Chloride)

37.1 g of trazodone (equal to about 0.100 mol) obtained according toexample 1 of U.S. Pat. No. 3,381,009 was put in a 500-ml flask togetherwith 140 ml of isobutyl alcohol. Then 100 ml of an aqueous solutioncontaining 5.3 g of Na₂CO₃ and 150 mg of benzyltriethylammonium chloridewas added, and the resultant mixture was heated to about 80° C. and leftat this temperature, with stirring, for about 2 hours.

Then the organic phase was separated from the aqueous phase and thenwashed with water. The residual water present in the organic phase wasremoved by azeotropic distillation. The resultant solution was cooled to5° C. to precipitate the crystals of trazodone base, which wereseparated by filtration.

The wet product (about 38.5 g) was dissolved in about 270 ml of acetone,heated until dissolution occurred, and then a 12N HCl aqueous solutionwas added to the solution until the pH was between 3 and 4 to salify thetrazodone base and obtain the corresponding hydrochloride.

The resultant solution was cooled to 5° C. to precipitate the crystalsof trazodone hydrochloride. The trazodone hydrochloride thus obtainedwas filtered, washed with acetone and dried at reduced pressure. At theend of drying, 36.7 g of trazodone hydrochloride was obtained (equal toabout 0.090 mol), at a product yield equal to about 90%.

TABLE 3 Alkylating substances N-(3- 1-bromo-3- chlorophenyl)-N′- 2,2-chloro- (3-chloropropyl)- dichloroethylamine propane piperazine Initialcontent 5 20 35 (ppm) Final content <0.46 <0.2 <0.04 (ppm)

EXAMPLE 4 Preparation in the Presence of Strong Base (KOH)

37.1 g of trazodone (equal to about 0.100 mol) obtained according toexample 1 of U.S. Pat. No. 3,381,009 was put in a 500-ml flask togetherwith 140 ml of methylisobutyl ketone. Then 100 ml of an aqueous solutioncontaining 2.8 g of KOH was added, and the resultant mixture was heatedto about 80° C. and left at this temperature, with stirring, for about 3hours.

Then the organic phase was separated from the aqueous phase and thenwashed with water. The residual water present in the organic phase wasremoved by azeotropic distillation. The resultant solution was cooled to5° C. to precipitate the crystals of trazodone base, which wereseparated by filtration.

The wet product (about 38 g) was dissolved in about 270 ml of acetone,heated until dissolution occurred, and then a 12N HCl aqueous solutionwas added to the solution until the pH was between 3 and 4 to salify thetrazodone base and obtain the corresponding hydrochloride.

The resultant solution was cooled to 5° C. to precipitate the crystalsof trazodone hydrochloride. The trazodone hydrochloride thus obtainedwas filtered, washed with acetone and dried at reduced pressure. At theend of drying, 35.5 g of trazodone hydrochloride was obtained (equal toabout 0.087 mol), at a product yield equal to about 87%.

TABLE 4 Alkylating substances N-(3- 1-bromo-3- chlorophenyl)-N′- 2,2-chloro- (3-chloropropyl)- dichloroethylamine propane piperazine Initialcontent 7 10 50 (ppm) Final content <0.46 <0.2 <0.4 (ppm)

The initial and final content of the alkylating substances shown in theabove Tables 1 to 4 was determined according to the followingprocedures.

Assay for the Determination of 2,2-Dichloroethylamine in TrazodoneHydrochloride by UV/Vis Spectrophotometry

The assay is based on the reaction of 2,2-dichloroethylamine with4-(4-nitrobenzyl)-pyridine according to a modified Friedman-Bogerprocedure as described in Anal. Chem. 33, 906-910, 1961, “Colorimetricestimation of nitrogen mustards in aqueous media”.

Briefly, a solution of 4-(4-nitrobenzyl)pyridine in acetone was added toan aqueous solution of trazodone hydrochloride (0.25 g/ml). Theresultant mixture was heated to 100° C. for 20 minutes, and then quicklycooled on an ice bath. 1 ml of acetone and 3 ml of 1N sodium hydroxidewere added to the solution. The coloured derivative was then extractedin chloroform (3 ml). The absorbance value at 544 nm was recordedagainst a blank sample, and the second derivative (δ) was calculatedfrom the value obtained. The content, in ppm, of 2,2-dichloroethylaminein the trazodone hydrochloride was found by using the external standardmethod.

The reaction was specific for 2,2-dichloroethylamine as no colouredderivative was obtained in the conditions described for other alkylatingagents such as 1-bromo-3-chloropropane andN-(3-chlorophenyl)-N′-(3-chloropropyl)-piperazine.

Linearity was verified from 1 to 10 ppm of 2,2-dichloroethylamine. Theaccuracy of the calibrators was always between 85 and 115% of thetheoretical value.

The lower limit of quantification (LLOQ) was set at 1 ppm based on thevalues of precision (measured as standard deviation, a) of the blank, asfollows: δ_(LLOQ)=δ_(blank)+10*σ=0.00048+10*0.00024=0.00288corresponding to 1.1 ppm.

The limit of detection (LOD) was set at 0.46 ppm, based on the values ofprecision (measured as standard deviation, σ) of the blank, as follows:δ_(LLOQ)=δ_(blank)+3*σ=0.00048+10*0.00024=0.00288 corresponding to 0.46ppm.

The precision was evaluated by calculating the coefficient of variation(CV %) of six determinations. The CV % at 5 ppm was equal to 12.2% andat 10 ppm it was equal to 11.2%.

Assay for the Determination of 1-Bromo-3-Chloropropane in TrazodoneHydrochloride by the Headspace Technique

The trazodone hydrochloride was dissolved in a water/methanol solution.After complete dissolution, the solution was put in a headspaceautosampler and the content of 1-bromo-3-chloropropane was determined bygas chromatography using a capillary column of medium polarity. Thecolumn effluent was monitored using a flame ionization detector. Thecontent of 1-bromo-3-chloropropane was determined as assay limitrelative to a standard sample with known content (2 ppm).

Chromatography conditions Gas chromatograph Trace Ultra Analyticalcolumn Capillary column, L = 30 m, inside diameter 0.53 mm, 3 μm (RTX1301 or equivalent) Stationary phase  6% cyanopropylphenyl, 94% dimethylpolysiloxane Oven temperature 90° C. per 2 min then increased to 130° C.at 10° C./min and maintained at 130° C. for 1 min Mobile phase(pressure) Nitrogen (100 kPa) Detector FID (air 350 kPa, hydrogen 35kPa) Retention time Approx. 3.5 min for 1-bromo-3-chloropropane Run time7 min Injector temperature 250° C. Detector temperature 250° C. Hydrogenpressure  35 kPa Air pressure 350 kPa

Conditions for the autosampler Headspace autosampler Perkin ElmerTurboMatrix 40 Operating mode continuous Diameter of transfer tube 0.25mm Sample temperature  90° C. Needle temperature 150° C. Temperature oftransfer tube 170° C. Time for thermostatic control 15 minutesPressurization time  1 minute

100 mg of trazodone hydrochloride was accurately weighed in a 22-ml testtube, then an aqueous solution of methanol at 0.025% (v/v) was added.The test tube was sealed with an aluminium crimp cap and PTFE coatedbutyl rubber septum and was then put in the headspace autosampler.

Linearity was verified from 0.2 to 9.3 ppm of 1-bromo-3-chloropropane,obtaining a correlation coefficient equal to 0.992 (by least squaresregression analysis).

The limits of detection (LOD) and the lower limit of quantification(LLOQ) were obtained from the signal/noise ratio (S/N) as follows:LOD=3×S/N=0.2 ppmLLOQ=10×S/N=0.5 ppm

The precision, determined on the basis of six repeat determinations, wasfound to be equal to 3.6% (CV) at 0.5 ppm.

The accuracy was determined as recovery %. Within the range of linearityit was always 100% with reference to the theoretical concentration.

Assay for the Determination of1-(3-Chlorophenyl)-4-(3-Chloropropyl)Piperazine (CCP) in TrazodoneHydrochloride by High-Performance Liquid Chromatography Coupled toTandem Mass Spectrometry (HPLC/MS/MS).

The trazodone hydrochloride was dissolved in water and injected into theanalyser. Chromatographic separation was obtained using a reversed-phaseanalytical column of the alkyl amide type.

The eluate from the column was monitored by positive-ion massspectrometry using the “Multiple Reaction Monitoring” (MRM) technique.

Chromatography conditions HPLC system Agilent series 1200 (orequivalent) Analytical column ABZ Plus, 75 × 4.6 mm, 3 μm (Supelco) Oventemperature 40° C. Solvent A Methanol Solvent B ammonium acetate 5 mM +0.1% (v/v) formic acid Operational flow rate 2 ml/min, a split was usedto reduce the flow at the ion source to 0.3 ml/min Elution IsocraticSolvent A/B = 12/88 (v/v) 3 min Purge Isocratic Solvent A/B = 80/20(v/v) 5 min Injection volume 5 μl Retention time Approx. 2.5 min for CCPRun time 10.0 min

Mass spectrometry conditions; Mass spectrometer Sciex API3000 LC/MS/MSSource Turbo Ion Spray ® Mode Positive-ion Detection Multiple ReactionMonitoring (MRM) Resolution Q1 low resolution (mass = 273.1 amu), Q3unit resolution (mass = 154.1 amu).

Linearity was verified from 0.4 to 8 ppm of1-(3-chlorophenyl)-4-(3-chloropropyl)piperazine, obtaining a correlationcoefficient equal to 0.9987 (by least squares regression analysis).

The accuracy was always between 85% and 115% of the theoretical value.

The lower limit of quantification (LLOQ) was set at 0.4 ppm based on thevalues of accuracy (85%) and precision (CV=6.7%) obtained from sixdeterminations.

The limit of detection (LOD) was set at 0.04 ppm based on the value ofthe signal/noise ratio (S/N): LOD=3×S/N=0.04 ppm.

1. A process for producing trazodone or trazodone hydrochloride, whichcomprises: (a) preparing an organic phase comprising trazodone in atleast one organic solvent; (b) preparing an aqueous phase comprising atleast one basic compound; (c) mixing said aqueous phase with saidorganic phase to obtain a mixture; (d) heating said mixture at atemperature of at least 40° C. for at least 30 minutes; (e) recoveringsaid trazodone; and, optionally, (f) treating said trazodone withhydrochloric acid to obtain trazodone hydrochloride.
 2. A processaccording to claim 1, wherein said trazodone or trazodone hydrochloridecomprises alkylating substances in a total amount which is less than 15ppm and said alkylating substances are selected from the groupconsisting of 2,2-dichloroethylamine, 1-bromo-3-chloro-propane,N-(3-chlorophenyl)-N′-(3-chloropropyl)-piperazine, and a mixturethereof.
 3. A process according to claim 2, wherein said trazodone ortrazodone hydrochloride comprises less than 10 ppm of said alkylatingsubstances.
 4. A process according to claim 2, wherein said trazodone ortrazodone hydrochloride comprises less than 2.5 ppm of said alkylatingsubstances.
 5. A process according to claim 2, wherein said trazodone ortrazodone hydrochloride comprises less than 1 ppm of said alkylatingsubstances.
 6. A process according to claim 1, wherein said organicsolvent is selected from the group consisting of an alcohol, an ether, ahydrocarbon, a ketone, and an ester.
 7. A process according to claim 6,wherein said organic solvent is selected from the group consisting ofethyl alcohol, propyl alcohol, isobutyl alcohol, hexyl alcohol, benzylalcohol, ethyl ether, propyl ether, toluene, benzene, xylene, acetone,methyl ethyl ketone, methyl isobutyl ketone, and ethyl acetate.
 8. Aprocess according to claim 1, wherein said organic phase comprises anamount of trazodone in the range from 10 g to 50 g per 100 grams oforganic phase.
 9. A process according to claim 1, wherein said aqueousphase comprises at least one basic compound selected from the groupconsisting of at least one inorganic base, at least one organic base,and a mixture thereof.
 10. A process according to claim 9, wherein saidinorganic base is selected from the group consisting of sodiumhydroxide, potassium hydroxide, sodium carbonate, potassium carbonate,sodium bicarbonate, potassium bicarbonate, sodium phosphate, potassiumphosphate, ammonium hydroxide, magnesium oxide, hydrazine, andhydroxylamine.
 11. A process according to claim 9, wherein said organicbase is selected from the group consisting of an aliphatic amine and anaromatic amine.
 12. A process according to claim 1, wherein said basiccompound is added in an amount in the range from 0.05 to 1 mol per moleof trazodone.
 13. A process according to claim 1, wherein said aqueousphase is added in an amount in the range from 30 g to 100 g per 100grams of organic phase.
 14. A process according to claim 1, wherein saidaqueous phase comprises a phase transfer catalyst.
 15. A processaccording to claim 14, wherein said phase transfer catalyst is selectedfrom the group consisting of a quaternary ammonium salt and a quaternaryphosphonium salt.
 16. A process according to claim 15, wherein saidquaternary ammonium salt is selected from the group consisting of benzyltributyl ammonium bromide, benzyl tributyl ammonium chloride, benzyltriethyl ammonium bromide, benzyl triethyl ammonium chloride, benzyltrimethyl ammonium chloride, cetyl pyridinium bromide, cetyl pyridiniumchloride, cetyl trimethyl ammonium bromide, didecyl dimethyl ammoniumchloride, dodecyl trimethyl ammonium bromide, dodecyl trimethyl ammoniumchloride, methyl tributyl ammonium chloride, methyl tributyl ammoniumhydrogen sulphate, methyl tricaprilyl ammonium chloride, methyl trioctylammonium chloride, phenyl trimethyl ammonium chloride, tetrabutylammonium borohydride, tetrabutyl ammonium bromide, tetrabutyl ammoniumchloride, tetrabutyl ammonium fluoride, tetrabutyl ammonium hydrogensulphate, tetrabutyl ammonium hydroxide, tetrabutyl ammonium iodide,tetrabutyl ammonium perchlorate, tetraethyl ammonium bromide, tetraethylammonium chloride, tetraethyl ammonium hydroxide, tetrahexyl ammoniumbromide, tetrahexyl ammonium iodide, tetramethyl ammonium bromide,tetramethyl ammonium chloride, tetramethyl ammonium fluoride,tetramethyl ammonium hydroxide, tetramethyl ammonium iodide, tetraoctylammonium bromide, tetrapropyl ammonium bromide, tetrapropyl ammoniumchloride, tetrapropyl ammonium hydroxide, tributyl methyl ammoniumchloride, and triethyl benzyl ammonium chloride.
 17. A process accordingto claim 15, wherein said quaternary ammonium salt is selected from thegroup consisting of tetrabutyl ammonium bromide, tetrabutyl ammoniumchloride, benzyl triethyl ammonium bromide, benzyl triethyl ammoniumchloride, benzyl trimethyl ammonium chloride, benzyl trimethyl ammoniumbromide, benzyl tributyl ammonium bromide, and benzyl tributyl ammoniumchloride.
 18. A process according to claim 15, wherein said quaternaryphosphonium salt is selected from the group consisting of benzyltriphenyl phosphonium bromide, benzyl triphenyl phosphonium chloride,butyl triphenyl phosphonium bromide, butyl triphenyl phosphoniumchloride, ethyl triphenyl phosphonium acetate, ethyl triphenylphosphonium bromide, ethyl triphenyl phosphonium iodide, hexadecyltributyl phosphonium bromide, methyl triphenyl phosphonium bromide,tetrabutyl phosphonium bromide, and tetraphenyl phosphonium bromide. 19.A process according to claim 15, wherein said aqueous phase comprises anamount of phase transfer catalyst in the range from 0.05 g to 0.5 g per100 grams of aqueous phase.
 20. A process according to claim 1, whereinsaid heating (d) is carried out at a temperature between 40° C. and theboiling point of the mixture of organic phase and aqueous phase, for aperiod of time between 30 minutes and 300 minutes.